1. Field of the Invention
The invention is in the field of electrophotographic reproduction machines, and particularly those machines controlled by digital computers.
2. Description of the Prior Art
Electrophotographic copying machines are well known within the prior art and typically employ mechanical or combinations of mechanical and electrical control logic for system control. Such control means is responsible for maintaining synchronism between the various operational stations of the reproduction machine and to ensure proper operation of the machine during the various operating modes. These control devices have become increasingly complex as the level of sophistication has increased within the reproduction machine itself. With the advent of variable magnification machines and color copiers the logical control means necessary to achieve proper synchronization and operation has become increasingly complex and expensive. Consequently, attempts to obtain efficient operation of these machines has developed utilizing digital computing device controllers which are programmed to carry out a sequence of operational tasks. Some of these digital device controls are quite specialized and govern only particular localized tasks or operations of the machine such as disclosed in U.S. Pat. No. 3,876,106. System operation as a whole has also been achieved in the prior art utilizing computers with relatively large CPU and memory storage units. Examples of these prior art devices are disclosed in U.S. Pat. Nos. 3,936,182, 3,914,047 and 3,940,210.
With the advent of larger and more complex photo-reproduction machines the various tasks needed to be performed by the machine have become increasingly large. Particularly, an operator may select from a variety of modes of operation, each one designating a particular sequence of operations which must be stored in the computer control means. In some cases the advantages of speed and efficiency of the computer control system has been outweighed by its prohibited cost and large physical dimensions required to store and execute programs defining the desired number and permutations of operational tasks. Still further cost and size restraints come into play when system flexibility is desired by way of expanding the computer control to various other controlled devices or operating stations as would be typical in the offering of a single model copier with various optional attachments. Thus, special purpose hardware may typically be employed as an alternative or addition to the utilization of the central digital computing controller.
Yet another disadvantage of the prior art in computer control devices lies in malfunctioning of the computers due to noise and radio frequency interference resulting primarily from the computer being exposed to the various electrical transients produced by operation of solenoids, motors, relays and the like. Consequently, there exists a need for an ever expanding digital computer capability and at the same time a need to isolate and remove the central controller from the environment of the reproduction machine to achieve error free operation.